The present invention concerns a novel system for detecting pacer mediated tachycardia.
In cardiac pacers in which electrical signals from the atrium are sensed and the ventricle is stimulated after a selected AV delay, the possibility of a pacer mediated tachycardia exists where there is retrograde conduction of the ventricular stimuli. To understand this phenomenon more clearly, reference is made to FIG. 1. For purposes of this discussion, it will be assumed that the pacer is operating in a demand mode, such as a DVI mode or a DDD mode. For simplicity, only the P waves and R waves of the heart's electrical waveform are illustrated. The upwardly-pointing arrows signify sensing and the downwardly-pointing arrows signify a stimulating pulse.
In FIG. 1 there is a normal heartbeat. The P wave is sensed at time 10 in the atrial channel and after an AV delay 14, the R wave is sensed at time 16 in the ventricular channel 18. Under these conditions, no pacing pulses are generated. In FIG. 2, however, there is AV block. Thus, the P wave is sensed in the atrial channel, but no R wave is sensed in the ventricular channel during a selected AV delay 14. Therefore, a stimulus is provided to the ventricle at time 16 which is the end of the selected AV delay.
FIG. 3 also illustrates an AV block situation. However, in FIG. 3 there is retrograde conduction 19 whereby the ventricular stimulus 20 conducts back to the atrium and, at time 22, the electrode in the atrium senses the retrograde P wave that has been caused by the pacer stimulus. Since no R wave is detected during the next AV delay 14a, at the end of the AV delay 14a another stimulus 24 is provided to the ventricle. Again, this other stimulus 24, if there is retrograde conduction, conducts back to the atrium causing the atrial electrode to sense another retrograde P wave at time 26. The cycle will repeat, resulting in tachycardia that is pacer mediated.
Referring now to FIG. 4, a heartbeat rate that is equal to the heartbeat rate of FIG. 3 is illustrated, although the FIG. 4 heartbeat is sinus tachycardia, not pacer mediated tachycardia.
It is, therefore, an object of the present invention to determine whether a detected tachycardia is pacer mediated.
Another object of one embodiment of the present invention is to modify the pacer operation in the event that the tachycardia is pacer mediated.
Other objects and advantages of the present invention will become apparent as the description proceeds.